Washington (CNN) -- Elena Kagan, building on a long, diverse legal career in government and academia, was officially sworn in as the 112th justice at the Supreme Court on Saturday, promising to "faithfully and impartially" discharge her new judicial duties.

With friends, family and four of her new colleagues looking on, the 50-year-old Kagan took the judicial oath in the court's wood-paneled West Conference Room. It was only the second time such a ceremony was televised at the court.

Chief Justice John Roberts administered the 62-word oath, required of all federal judges. In a private ceremony just moments before, Kagan took a separate constitutional oath across the hall. Both are necessary for her lifetime job to become official.

Kagan beamed as she waved to relatives and guests when walking in for the public ceremony. Among those in the ornate room were her two brothers, as well as former colleagues from the Justice Department, where she served as solicitor general before being tapped by President Obama for the high court on May 10.

The Bible used in the two-minute ceremony is owned by Justice Stephen Breyer, who was not in attendance.

Roberts told the audience of about 70 that Kagan can "assume her duties as an associate justice and begin work right away."

"Congratulations," he said afterward to rousing cheers. "On behalf of my colleagues, welcome to the court. We look forward to serving with you in our common calling."

Kagan made no statements and did not answer questions.

The newest justice can now start moving into her chambers and preparing for the upcoming fall term. The court is in the middle of a three-month recess, but Kagan must be available to handle any emergency appeals, such as a request for a stay of execution.

Kagan will soon formally hire four law clerks. She also will have two secretaries and a messenger to assist her.

Justices Anthony Kennedy, Clarence Thomas, Ruth Bader Ginsburg and Sonia Sotomayor were on hand for the swear-in ceremony. So, too, was John Paul Stevens, whom Kagan replaces on the bench.

Special guests were Cissy and Thurgood Marshall Jr., the widow and son of the late Justice Thurgood Marshall. The diminutive Kagan clerked for him in 1987-88, where she earned the affectionate nickname "Shorty" from the legal and judicial pioneer.

The Senate confirmed Kagan 63-37 on Thursday on a mostly party-line vote. Obama, who did not attend the swearing-in, hosted his nominee at a White House reception Friday, telling her that as the third woman on the current court, it "will be a little more inclusive, a little more representative, more reflective of us as a people than ever before."

Kagan in her brief remarks at the White House promised "to work my hardest and try my best to fulfill these commitments and to serve this country I love as well as I am able."

Democrats continued to praise Kagan as an accomplished, articulate lawyer who had earned support from people across the political spectrum. Many Republicans cited her lack of judicial experience, and predicted she would become a judicial "activist," reinterpreting the law to conform with her own liberal political beliefs.

Kagan was born in New York City in 1960, one of three children of a lawyer father and schoolteacher mother. She graduated from Princeton University undergraduate and Harvard Law School.

While never a judge herself, Kagan's résumé is broad: work on Michael Dukakis' 1988 presidential campaign; a lawyer in private practice for two years; stints as a law professor and later, dean; four years as a legal and policy adviser in the Clinton White House; and most recently as solicitor general in the Obama Justice Department.

She supervised every federal appeal presented to the high court during her 16 months in the administration, and personally argued six cases before the same justices she will now count as colleagues.

Kagan joins a closely divided court that often splits in favor of a shaky 5-4 conservative majority. Despite no judicial record to draw clues on the kind of justice she would become, White House officials had quietly assured allies Kagan would be a "reliable" liberal vote similar to Stevens, the well-respected unofficial leader of the left-leaning bloc of the court.

She is, therefore, not expected to tilt the current ideological balance on the high court.

Among the cases she will confront in her first term beginning in October will be disputes over noisy protests at military funerals, state bans on violent video games and the death penalty. High-profile appeals that may reach the court in the next couple of years include Arizona's sweeping immigration reform law; California's ban on same-sex marriage; and a challenge to health care mandates passed by Congress this spring.

Here are the two oaths Elena Kagan took Saturday:

Constitutional oath: "I do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter: So help me God."

Judicial oath: "I do solemnly swear (or affirm), that I will administer justice without respect to persons, and do equal right to the poor and to the rich, and that I will faithfully and impartially discharge and perform all the duties incumbent on me, under the Constitution and laws of the United States. So help me God."